1. FIELD OF THE INVENTION
The present invention relates to an apparatus for facilitating a flow through a hopper of solid particulates and pertains more particularly to an apparatus for facilitating a flow through a hopper of fibrous or irregularly shaped solid particulates at a substantially constant mass flow rate.
2. DESCRIPTION OF THE PRIOR ART
It is a common industrial procedure to have solid particulate feed material flow through a hopper. In a typical hopper system, an auger at a bottom of the hopper rotates to deliver feed material through an orifice. Ideally, a rate at which the auger turns determines a flow rate of the feed material. A mechanical agitator may be used to fluidize particulates above the auger. Ideally, the feed material is of uniform bulk density and flows through the hopper with a constant mass flow rate. These ideal conditions are very difficult to attain, especially with material that is fibrous or irregularly shaped such as wood flour or sawdust. These materials have a high angle of repose and tend to form self-supporting stable arches above the agitator while the fluidized solids at the auger are depleted, so that the mass flow rate through the auger decreases and eventually approaches zero. Alternatively, the arch may collapse and form a vertical "chimney" in the particulate, whose walls are self-supporting, giving rise to the same difficulty.
Various devices have been used to break up the arches and chimneys. These devices have typically involved agitation of the hopper or large proportions of the hopper contents or both. For example, a vertical shaft inside the hopper may be provided with a plurality of horizontal rods distributed along a length of the shaft, and the entire apparatus may be vibrated or rotated to prevent agglomeration of the feed material. Another device provides bladders inside the hopper that are inflated to collapse a bridge formed in the feed. Both of these devices generally require undesirably large quantities of energy to work properly. Furthermore, in hoppers in which the auger speed is electronically controlled to be responsive to the mass flow rate, extreme agitation can disrupt a normal operation of the electronic system.